Tailoring the Morphology of a Diketopyrrolopyrrole‐based Polymer as Films or Wires for High‐Performance OFETs using Solution Shearing

Abstract

Conjugated polymers often show efficient charge carrier transport along their backbone which is a primary factor in the electrical behavior of Organic Field Effect Transistor (OFETs) devices fabricated from these materials. Herein, a solution shearing procedure is reported to fabricate micro/nano wires from a diketopyrrolopyrrole (DPP)‐based polymer. Millimeter to nanometer long polymer wires orientated in the coating direction are developed after a thorough analysis of the deposition conditions. It shows several morphological regimes—film, transition, and wires and experimentally derive a phase diagram for the parameters coating speed and surface energy of the substrate. The as‐fabricated wires are isolated, which is confirmed by optical, atomic force, and scanning electron microscopy. Beside the macroscopic alignment of wires, cross‐polarized optical microscopy images show strong birefringence suggesting a high degree of molecular orientation. This is further substantiated by polarized UV‐Vis‐NIR spectroscopy, selected area electron diffraction transmission electron microscopy, and grazing‐incidence wide‐angle X‐ray scattering. Finally, an enhanced electrical performance of single wire OFETs is observed with a 15‐fold increase in effective charge carrier mobility to 1.57 cm2 V−1 s−1 over devices using films (0.1 cm2 V−1 s−1) with similar values for on/off current ratio and threshold voltage.